A heavy goods vehicle tire comprises a crown portion that is extended on each side by sidewalls ending in beads. Such a tire comprises a plurality of reinforcements including, in particular, a carcass reinforcement the role of which is to withstand the forces created by the internal inflation pressure of the tire. This carcass reinforcement is situated in the crown and sidewalls of the tire and is anchored at its ends to suitable anchoring structures located in the beads. The carcass reinforcement is generally composed of a plurality of reinforcing elements arranged parallel to one another and making an angle of close or equal to 90 degrees with the circumferential direction (in this case, the carcass reinforcement is said to be “radial”). The carcass reinforcement is usually anchored by being turned up around an anchoring structure having a suitable circumferential stiffness, in order to form axially on the outside a turn-up portion the length of which, measured for example with respect to the radially innermost point of the anchoring structure, is chosen to provide satisfactory endurance to the tire during use. Axially between the turn-up portion and the main portion of the carcass reinforcement there are one or more elastomer-based materials which provide mechanical coupling between the two portions of the carcass reinforcement.
In use, such a tire is mounted on a mounting rim comprising rim seats designed to be in contact with the radially innermost parts of the beads and, axially on the outside of each seat, a rim flange for fixing the axial position of said bead when the tire is mounted and inflated to its nominal pressure.
In order to make the tire withstand the mechanical stresses of rolling, it is known practice to provide additional bead reinforcements in particular in the form of plies arranged against at least part of the turn-up portion of the carcass reinforcement.
During rolling, the tire beads are subjected to a large number of bending cycles, as they wind around the rim flanges (i.e. they partly adopt the geometry of said flanges). This bending results in larger or smaller variations in curvature combined with variations in tension in the bead reinforcements and in particular in the turn-up portion of the carcass reinforcement. These same cycles induce compressive and extensile forces in the materials constituting the beads. During rolling, a cyclical circumferential displacement of the reinforcing elements of the reinforcement of the carcass reinforcement can also be seen in the sidewalls and the beads of the tire. A cyclical circumferential displacement is understood here to mean that displacement occurs in one direction and in the opposite direction with respect to a mean position of equilibrium each time the wheel rotates.
Rolling generates stresses and/or deformations in the materials constituting the bead, in particular the elastomers and more particularly those which are located in the immediate vicinity of the ends of the reinforcements (the end of the turn-up portion of the carcass reinforcement or the ends of the additional reinforcements). These stresses and/or deformations may lead to a more or less substantial reduction in the service life of the tire.
This is because these stresses and/or deformations may cause detachment and cracks near the ends of said reinforcements. Owing to the radial orientation of the reinforcing elements and to the nature of said reinforcing elements (in general, these are metal cables) of which it is made, the end of the turn-up portion of the carcass reinforcement is particularly sensitive to this phenomenon.
The document published under the reference WO 2006/013201-A1 describes a tire bead structure in which the carcass reinforcement is no longer turned up by being partially wrapped around a bead wire but is wound at least one complete revolution around an anchoring structure in each of the beads. In this manner, the end of the carcass reinforcement is located in an area of the bead which is not subjected to strong cyclical stresses; it is thus possible to increase the endurance of the beads.
However, while such a tire bead structure is effective from a mechanical point of view, it is nonetheless still expensive and difficult to implement using conventional industrial manufacturing means.
In a different approach, a means has been sought to prevent the risks of bead deterioration by proposing a bead structure having sufficient stiffness to withstand the bending forces and the circumferential movements of the reinforcements during rolling which is also easy to implement and economically attractive to produce on an industrial scale.
The document published under the reference WO 2008/107234-A1 describes such a bead structure. The document discloses a heavy goods vehicle tire comprising a tread extended transversely on each side by sidewalls ending in beads designed to engage with a mounting rim. In addition, this tire comprises a radial carcass reinforcement formed from a plurality of reinforcing elements directed in a direction that makes an angle of at least 80 degrees with the circumferential direction.
This carcass reinforcement is anchored in each of the beads to an anchoring structure comprising a circumferential reinforcement around which a coating profiled element is formed of which the perimeter of the radial section comprises a part radially on the inside and a part radially on the outside, these two parts meeting at the two axially furthest apart points of the perimeter of said coating profiled element.
Moreover, this carcass reinforcement is partially wrapped around the coating profiled element of the anchoring structure, proceeding from the inside of the tire to the outside, the end of this carcass reinforcement being located on or near the perimeter of the coating profiled element.
This tire also comprises a first connecting reinforcement formed from a plurality of reinforcing elements directed in a direction that makes an angle of greater than or equal to 70 degrees with the circumferential direction. This first connecting reinforcement comprises a first part in contact with the carcass reinforcement between (i) a point radially on the outside with respect to the perimeter of the coating profiled element of the radially outermost anchoring structure and (ii) the end point of the carcass reinforcement, this first connecting reinforcement being extended beyond the end of the carcass reinforcement by a second part in contact with the coating profiled element as far as a point located on the part radially on the outside of the perimeter of the coating profiled element.
This tire furthermore comprises a second connecting reinforcement surrounding the first connecting reinforcement and running radially under the coating profiled element radially on the inside of said first connecting reinforcement in order to form an internal portion and an external portion, the internal portion being located axially on the inside with respect to the carcass reinforcement and the external portion being located axially on the outside of said carcass reinforcement; the internal portion is in contact over a non-zero length with the carcass reinforcement between a first end point of the first portion and the end point of the first connecting reinforcement, the external portion being in contact with the carcass reinforcement from one point to an end point of the external portion over a non-zero length, these points being located radially outside the end points of the first connecting reinforcement.
This second connecting reinforcement is formed from a plurality of reinforcing elements directed in a mean direction that makes an angle of at most 50 degrees with the circumferential direction.
What distinguishes the architecture of this tire is, inter alia, the fact that the second connecting reinforcement is anchored around the bead anchoring structure while at the same time being coupled to the carcass reinforcement axially on each side of this reinforcement, in combination with the end of the carcass reinforcement being positioned in the vicinity of the anchoring structure. In such a structure, the end of the carcass reinforcement is kept in an area subjected to fairly low amounts of stress and deformation under running conditions and this end is moreover covered by at least the second reinforcement.
While such an architecture allows bead deterioration to be significantly reduced, there is still an area subject to a high concentration of crack-initiating stresses radially on the inside of the anchoring structure.